Communication systems in a related technology, for example, Long Term Evolution (LTE) and Worldwide Interoperability for Microwave Access (WiMax) and 802.11n, all adopt a 2nd-Dimensional (2D) Multiple-Input Multiple-Output (MIMO) technology, of which a basic principle is to improve transmission quality and increase a system capacity by a degree of freedom of a 2D space on a horizontal plane. Along with development of an antenna design architecture, for improving transmission efficiency of a mobile communication system and improving a user experience, it is necessary to fully explore a degree of freedom of a perpendicular space to extend the 2DMIMO technology to a 3rd-Dimensional (3D) MIMO technology and improve system performance by fully utilizing a degree of freedom of a 3D space.
A 2DMIMO antenna architecture adopts multiple array elements in a perpendicular dimension, thereby obtaining a higher antenna gain. While each antenna array element in the perpendicular dimension adopts a fixed weight to ensure that a required beam pattern is obtained in the perpendicular dimension. Therefore, it is impossible for the 2DMIMO technology to implement beamforming in the perpendicular dimension.
For fully utilizing a MIMO technology in the perpendicular dimension, 3DMIMO may control weighting factors of different antenna array elements in the perpendicular dimension to form different beams. The beams in the perpendicular dimension may be effectively distinguished, thereby providing multiple-user multiplexing in the perpendicular dimension and increasing a capacity. An LTE system supports a design of maximally 8 antennae, and 3D MIMO extends a channel number of an antenna, and supports a 3D antenna form with a channel number of 16, 32, 64, 128 and the like.
In an existing standard, there are multiple CSI-RS patterns. For example, in a 2-port Frequency Division Duplexing (FDD) system, there are 20 patterns, and the specific CSI-RS pattern to be adopted is notified to UE through high-layer signaling. In each pattern, CSI-RSs are sent through each resource block of the whole bandwidth. Herein, as shown in FIG. 1, there are 5 patterns in an 8-port (numbered to be 0, 1, 2, 3, 4, 5, 6 and 7 respectively and corresponding to CSI-RS port serial numbers 15˜22) FDD system, herein a set of cells with the same mark (for example, “\” and “/”) represents a pattern.
UE in the related technology feeds back Channel State Information (CSI) according to CSI-RS channel estimation. For an 8-antenna system in the related technology, a codebook set defined in a standard is optimally designed according to an 8-polarized-antenna form. 8 dual-polarized antennae in a horizontal dimension are considered. A numbering rule is usually as follows: as shown in FIG. 2, numbering is started from the same polarization direction, and then is performed in another polarization direction, herein the same sign is adopted to represent the same antenna polarization direction, figures below the antennae represent numbers of the antennae, and the numbers of the 8 antennae are sequentially 0, 1, 2, 3, 4, 5, 6 and 7.
During large-scale antenna 3D MIMO standardization, a CSI-RS pattern enhancement direction is mainly 16 ports, and 3D MIMO of a larger channel number is implemented by beamformed CSI-RSs, so that an excessive CSI-RS overhead is avoided. Design of a CSI-RS pattern of 16 ports is being discussed by existing standardization. At present, a 16-channel antenna form which is mainly considered is 4H2V (4 horizontal polarized antennae and 2 channels in a perpendicular direction). Considering a codebook design, a specific numbering rule is as follows: as shown in FIG. 3, numbering is started from the same polarization direction, and then is performed in another polarization direction, herein the same sign is adopted to represent the same antenna polarization direction, figures below antennae represent numbers of the antennae, and the numbers of the 16 antennae are sequentially 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 and 15.
At present, a main CSI-RS pattern design direction is combination of existing CSI-RSs of 8 ports into CSI-RSs of 16 ports. Under this situation, when a base station sends CSI-RSs of 16 ports, there exists the problem of how to feed back accurate CSI by conventional UE (UE with 8 ports).
There are two solutions in the related technology, herein, in the first solution, the base station sends two sets of CSI-RSs, i.e., CSI-RSs of 16 ports+8 ports (or 2 and 4 ports). This solution has the shortcoming that the base station sends the two sets of CSI-RSs, so that a Resource Element (RE) overhead is increased.
In the second solution, the base station sends a set of CSI-RSs of 16 ports, notifies a CSI-RS pattern of 16 ports to new UE (UE with 16 ports) and notifies a CSI-RS pattern of 8 ports (or 2 and 4 ports) to conventional UE. Then, CSI-RSs read by the conventional UE are sent by antennae 0˜7. However, an existing 8-antenna codebook is designed according to a dual-polarized antenna form. Therefore, this solution may not achieve relatively high compatibility with CSI measurement of the conventional UE.